1. Field of the Invention
The present invention relates in general to an optical measuring apparatus or instrument adapted to measure or determine electric quantities such as quantities of current, magnetic field, voltage and electric field associated with power transmission and distribution lines, electric wirings and other electric parts, and an ambient temperature of these components, by utilizing a beam of light as a medium for the measurement. More particularly, the invention is concerned with such an optical measuring instrument capable of concurrently measuring or determining a temperature and at least one electric quantity.
2. Discussion of the Prior Art
In recent years, optical measurement utilizing a light beam as a medium having high degrees of insulation and freedom from electromagnetic induction noises has been drawing growing attention of the industries concerned with the art of power transmission and distribution, for measuring or determining an electric current, a magnetic field strength, a voltage, an electric field strength or other electric quantity associated with power transmission and distribution lines, together with the ambient temperature. Examples of such optical measuring instruments recently proposed include optical voltage/electric-field sensors utilizing a Pockel's effect, optical current/magnetic-field sensors utilizing a Faraday effect, temperature sensors of optical path shielding type adapted to shield an optical path with a shielding ratio changing depending upon the ambient temperature, and temperature sensors of optical intensity modulation type adapted to change an amount of light beam transmitted through a substance placed on an optical path, depending upon the ambient temperature.
In the field of electric power transmission and distribution, facilities for transmitting and distributing electric power are becoming more and more large-sized and complicated, to meet a recent increasing demand for the electric power and a recent growing need for power distribution to an increasing number of points of consumption per unit area. Accordingly, monitoring of the power transmission and distribution lines is becoming more and more important. To this end, there is an increasing requirement for obtaining useful information concerning the conditions of the power transmission and distribution lines.
Conventional optical measuring sensors are a single-purpose sensor adapted to measure or determine only one physical quantity. If there are two or more or many physical quantities to be measured, the number of optical sensors required accordingly increases. This makes it difficult to provide a compact measuring instrument or apparatus capable of measuring two or more quantities.
Although a measuring instrument may accommodate in a relatively compact fashion a plurality of sensors disposed in parallel with each other, the compactness of the instrument is undesirably limited since the individual sensors are structurally independent of each other. Further, the number of optical paths along which a measuring light beam from the sensing head portion of each sensor is propagated to the light-sensitive portion of the sensor is equal to the number of the sensors. This results in a relatively large number of optical fibers, which are widely used as the optical paths in the fields of power transmission and distribution. Where the optical fibers are supported extending through ceramic insulators, the durability of the ceramic insulators is deteriorated, for example.
In the above case where a relatively large number of optical fibers are used for directing the measuring light beams from respective sensors, the required size of holes formed through the ceramic insulators for supporting the optical fibers must be accordingly large. The increased size of the holes causes reduced strength of the insulators, leading to easy structural deterioration or breakage of the insulators.